In a positive displacement fluid pump commonly referred to as a gerotor pump, a ring gear and a pinion gear inside of the ring gear are supported on a pump housing for rotation about parallel, laterally separated centerlines. A plurality of pump chambers defined by the teeth of the ring and pinion gears expand in an inlet half of a crescent-shaped cavity between the ring and pinion gears and collapse in a discharge half of the crescent-shaped cavity. An inlet port in a first side wall of the pump housing faces the inlet half of the crescent-shaped cavity. A discharge port in an opposite second side wall of the pump housing faces the discharge half of the crescent-shaped cavity. The inlet and the discharge ports are separated angularly or "timed" to prevent the pump chambers from simultaneously overlapping both the inlet port and the discharge port. The bulk modulus of the fluid being pumped and the timing between the inlet and the discharge ports affect the performance of gerotor pumps. For high bulk modulus fluids, i.e. fluids having insubstantial volumes of entrained vapor bubbles, minimum port timing is desirable because mechanical compression of the fluid trapped between the inlet and the discharge ports may create noise inducing pressure spikes. For lower bulk modulus fluids, i.e. fluids having significant volumes of entrained vapor bubbles, increased port timing promotes mechanical compression of the trapped fluid to collapse the vapor bubbles in the pump chamber instead of in the discharge port where such collapse may create noise inducing pressure pulses. In an application such as a motor vehicle fuel pump where the bulk modulus of the fluid being pumped, e.g. gasoline, may be low in hot weather and high in cold weather, timing the ports for one of high and low bulk modulus fluid may negatively impact the performance of the fuel pump when the other is being pumped. A gerotor pump according to this invention is an improvement over prior gerotor pumps having port timing for only one of high and low bulk modulus fluid.